1. Field of the Invention
The present invention relates to a III-nitride semiconductor optical device, and an epitaxial substrate for the III-nitride semiconductor optical device.
2. Related Background Art
Non Patent Literature 1 discloses uniform growth of (1-101)-plane GaN on a silicon substrate. This GaN is grown on coalesced stripes of GaN grown by selective metal-organic vapor phase epitaxy on a 7-degree off-axis (001)Si substrate via an AlN intermediate layer. Three types of Samples (A), (B), and (C) were produced. Sample (A) contains GaN grown on an LT-AlN intermediate layer. Sample (B) contains a 30-nm Al0.1Ga0.9N upper layer. Sample (C) contains GaN grown without the LT-AlN intermediate layer. Hall measurements were carried out with the three types of Samples (A), (B), and (C). Sample (A) exhibited p-type conduction and Sample (B) n-type conduction. Sample (C) exhibited n-type, p-type, and n-type conductions in three respective temperature regions (not more than 80 K, 80 K to 200 K, and not less than 200 K) from low temperature to high temperature. Non Patent Literature 1 discloses the following: Samples (A) and (B) contain GaN/AlN/Si hetero-junctions, and the conduction in the hetero junctions is presumed to be the major conduction in Samples (A) and (B).
Non Patent Literature 2 discloses uniform growth of (1-101)-plane GaN on a silicon substrate. This GaN was grown on coalesced stripes of GaN grown by selective metal-organic vapor phase epitaxy on a 7-degree off-axis (001)Si substrate via an AlN intermediate layer. (1-101)-plane GaN was doped with magnesium. For doping with magnesium, a dopant gas EtCp2Mg was used. In a doped region where a molar ratio of dopant gas/gallium source (EtCp2Mg/TMG) is less than 2×10−3, the hole concentration in the GaN film decreases with increase in doping amount of the dopant gas. On the other hand, in a doped region over the molar ratio of 2×10−3, the hole concentration increases with increase in doping amount of the dopant gas and becomes saturated at about 1×1018 cm−3. In growth of c-plane GaN, the grown GaN film in the doped region with the molar ratio of less than 2×10−3 demonstrated n-type conduction, but the grown GaN film in the doped region with the molar ratio of more than 2×10−3 demonstrated p-type conduction. Non Patent Literature 2 explains this phenomenon as follows: (1-101)-plane GaN consists of a nitrogen plane whereas c-plane GaN consists of a Ga-plane.
Non Patent Literature 3 discloses uniform growth of (1-101)-plane and (11-22)-plane GaN on a silicon substrate. Carbon is added in growth of GaN, using a dopant gas C2H2. The doping of (11-22)-plane GaN with carbon provides the effect different from that by the doping of (1-101)-plane GaN with carbon.
Some of the authors of Non Patent Literatures 1-3 are the same.
Patent Literature 1 discloses increase in electric resistance of GaN film by increase in carbon concentration.
Patent Literature 1: Japanese Patent Application Laid-open No. 2009-21279
Non Patent Literature 1: T. Hikosaka et al., Applied Physics Letters Vol. 84, No. 23 (2004) pp. 4717-4719.
Non Patent Literature 2: Nobuhiro Sawaki et al., Journal of Crystal Growth 298 2007, pp. 207-210.
Non Patent Literature 3: Nobuhiro Sawaki et al., Journal of Crystal Growth 311 2009, pp. 2867-2874.